The field of the present invention is fuel rails for internal combustion engines and in particular, fuel rails for reciprocating piston, spark-ignited internal combustion engines.
In the past three decades, there have been major technological efforts to increase the fuel efficiency of automotive vehicles. One technical trend to improve fuel efficiency has been to reduce the overall weight of the vehicle. A second trend to improve fuel efficiency has been to improve the aerodynamic design of a vehicle to lower its aerodynamic drag. Still another trend is to address the overall fuel efficiency of the engine.
Prior to 1970, the majority of production vehicles with a reciprocating piston gasoline engine had a carburetor fuel supply system in which gasoline is delivered via the engine throttle body and is therefore mixed with the incoming air. Accordingly, the amount of fuel delivered to any one cylinder is a function of the incoming air delivered to a given cylinder. Airflow into a cylinder is effected by many variables including the flow dynamics of the intake manifold and the flow dynamics of the exhaust system.
To increase fuel efficiency and to better control exhaust emissions, many vehicle manufacturers went to port fuel injection systems, where the carburetor was replaced by a fuel injector that injected the fuel into a port which typically served a plurality of cylinders. Although port fuel injection is an improvement over the prior carburetor fuel injection system, it is still desirable to further improve the control of fuel delivered to a given cylinder. In a step to further enhance fuel delivery, many spark ignited gasoline engines have gone to a system wherein there is supplied a fuel injector for each individual cylinder. The fuel injectors receive their fuel from a fuel rail, which is typically connected with all or half of the fuel injectors on one bank of an engine. Inline 4, 5 and 6 cylinder engines typically have one bank. V-block type 6, 8, 10 and 12 cylinder engines have two banks.
One critical aspect of a fuel rail application is the delivery of a precise amount of fuel at a precise pressure. In an actual application, the fuel is delivered to the rail from the fuel pump in the vehicle fuel tank. At an engine off condition, the pressure within the fuel rail is typically 45 to 60 psi. When the engine is started, a typical injector firing of 2-50 milligrams per pulse momentarily depletes the fuel locally in the fuel rail. Then the sudden closing of the injector creates a pressure pulse back into the fuel rail. The injectors will typically be open 1.5-20 milliseconds within a period of 10-100 milliseconds.
The opening and closing of the injectors creates pressure pulsations (typically 4-10 psi peak-to-peak) up and down the fuel rail, resulting in an undesirable condition where the pressure locally at a given injector may be higher or lower than the injector is ordinarily calibrated to. If the pressure adjacent to the injector within the fuel rail is outside a given calibrated range, then the fuel delivered upon the next opening of the injector may be higher or lower than that preferred. Pulsations are also undesirable in that they can cause noise generation. Pressure pulsations can be exaggerated in a returnless delivery system where there is a single feed into the fuel rail and the fuel rail has a closed end point.
To reduce undesired pulsations within the fuel rails, many fuel rails are provided with added pressure dampers. Dampers with elastomeric diaphragms can reduce peak-to-peak pulsations to approximately 1-3 psi. However, added pressure dampers are sometimes undesirable in that they add extra expense to the fuel rail and also provide additional leak paths in their connection with the fuel rail or leak paths due to the construction of the damper. This is especially true with new Environmental Protection Agency hydrocarbon permeation standards, which are difficult to satisfy with standard O-ring joints and materials. It is desirable to provide a fuel rail wherein pressure pulsations are reduced while minimizing the need for dampers.
Fuel rail systems have been developed which have reduced or eliminated the need for add on diaphragms or dampers. In one such fixed rail system, a compact fuel body is provided with a pulsating damping wall. The compact body is fluidly connected with various injector cups by flexible fuel tubes. This fuel rail system has been found to offer certain disadvantages.
The first disadvantage is that the damping wall is spaced away from the injector cup. Maximum damping efficiency occurs by having the damping wall as close as possible to the injector cup. The second disadvantage is the compact body with the flexible fuel tubes will typically include a type of high-temperature-resistant polymeric material that has a tendency to degrade in the high temperature environment adjacent to an engine. Additionally, brazing subsequent to fabrication often cannot be allowed since the temperature required for brazing will damage the flexible tubes. Accordingly, brazing of the compact body must be performed before connecting the flexible tubes to the compact body.
In an attempt to overcome the disadvantages associated with the compact fuel body with flexible fuel tubes there has come forth a fuel rail system having a generally thin wall rectangular tube which typically will have a height/width ratio of 1.5 to 2.0 or greater. The thin wall of the rectangular tube fuel rail system deflects upon pressure pulsations and acts as a damper. The thin wall rectangular tube design fuel rail system has some advantages over the compact body development in that the flexible fuel tubes may, in some instances, be eliminated. However, the rectangular thin wall tube design also brings forth certain disadvantages. The thinness of the flexible tube is limited by the structural rigidity that is required of the tube for its attachment to the engine. Additionally, the thin wall tube is hard to bend. Often a straight line is not a preferred configuration of the fuel rail due to other engine electrical and fluid conduits provided in the engine compartment. Another disadvantage of the prior invention is that the thinness of the thin wall rectangular tube can have excessive vibration or noise at certain frequencies of engine operation.
It is desirable to provide a fuel rail system that eliminates the requirement for add-on dampers which overcomes the noise problems associated therewith and prior vibration and noise. It is also desirable to provide a fuel rail system that can be brazed at late stages of assembly.
To make manifest the above-noted and other manifold desires, a revelation of the present invention is brought forth. In a preferred embodiment, the present invention provides a fuel rail for a plurality of fuel injectors. The fuel rail includes a sealed housing having a fuel inlet and at least two injector outlets. The sealed housing is formed by a first stamped male metallic member. The first member has a first thickness and at least first and second injector outlets delivering fuel to fuel injectors. Fixedly connected with the male member adjacent the injector outlets are injector cups. A bracket is provided which is fixedly connected to the first member (typically by welding) to connect the fuel rail to the internal combustion engine.
A second stamped female metallic member is provided and is sealably connected to the first member to form a control volume therewith. The second member has a second thickness that is materially lower than the first thickness of the first member. Accordingly, the second member has a wall to damp pulsations caused by the opening and closing of the injectors.
Further features and advantages of the present invention will become more apparent to those skilled in the art after a review of the invention as it shown in the accompanying drawings and detailed description.